The present invention pertains to a composition in the form of a stable hydroalcoholic polyurethane dispersion containing polymers. The composition exhibits film-forming properties and can be formulated to have anti-microbial activity.
Polyurethane is a generic term used to describe polymers prepared by the reaction of a polyfunctional isocyanate with a polyfunctional alcohol to form urethane linkages. The term xe2x80x9cpolyurethanexe2x80x9d has also been used more generically to refer to the reaction products of polyisocyanates with any polyactive hydrogen compound including polyfunctional alcohols, amines, and mercaptans. Polyurethanes are used in a variety of applications including as elastomers, adhesives, coatings, and impregnating agents.
For coating applications, polyurethane polymers can be dispersed in water by incorporating stabilizing groups into their backbone. Anionic, cationic and non-ionic dispersion stabilizing groups have been used. Various aqueous polyurethane dispersions have been prepared by those skilled in the art. For example, U.S. Pat. No. 3,479,310 (Dieterich et al.) discloses water-dispersed polyurethane polymers suitable for uses as waterproof coatings. The polymer is prepared from polyhydroxy compounds, polyisocyanates, optional chain lengthening agents, and a sufficient amount of a component having an ionic salt-type group. U.S. Pat. No. 4,307,219 (Larson) discloses dispersible polyurethane resin prepared by reaction of hydrophilic diols, hydrophobic diols, diisocyanates, and, optionally, chain extenders. Such a urethane resin can be used as protective coatings, primers, and binders.
Although aqueous dispersions of polyurethanes have been widely disclosed, the inventors are not aware of any references to stable polyurethane dispersions in alcohol-water solvent systems, particularly when prepared from very hydrophobic polyols. Polyurethane dispersions in hydro-alcohol (i.e., alcohol-water) systems are especially difficult for at least two reasons.
First, the addition of lower alcohols (e.g., C1 to C4) to water decreases the surface tension of the solvent system. For example, a 40 weight percent (wt %) ethanol in water system has a surface tension of about 31 dyne/cm compared to a pure water system, which has a surface tension of about 72 dyne/cm at about 20xc2x0 C. A 60 wt % ethanol in water system has a surface tension of 27 dyne/cm at about 20xc2x0 C. The reduction in surface tension can affect the ability to self assemble hydrophilic and hydrophobic domains during the dispersion preparation. Second, many of the polyurethane components (i.e., the starting reactants) are soluble in hydro-alcohol solvent systems, which result in solutions and not dispersions. Polymer solutions have substantially higher viscosity than polymer dispersions, making them harder to process in certain operations, such as coating and spraying operations. Polymer solutions also tend to achieve lower percent solids when compared to polymer dispersions, making the former less attractive during coating operations and during shipping. Lower solids solutions also require longer drying times than dispersions to form a film because of the greater amount of solvent present the higher affinity of the polymer for that solvent, and the immediate formation of a xe2x80x9cskinxe2x80x9d on the surface of the film as it begins to dry. Furthermore, the molecular weight of soluble polymers is often much lower than that of dispersions.
U.S. Pat. No. 4,507,430 (Shimada et al.) discloses a water-based polyurethane emulsion that comprises a hydrogenated polyalkadiene polyol component and a polyisocyanate component. Shimada discloses that the materials are useful as an adhesive or coating material for a polyolefin resin, and can be applied wet and dried or bonded by dry lamination requiring heat and pressure. While the hydrogenated polyalkadiene polyol component of Shimada is alcohol-water insoluble, there was no disclosure of polyurethane dispersions in hydro-alcohol solvent system.
U.S. Pat. No. 5,672,653 (Frisch et al.) discloses an anionic waterborne polyurethane dispersion prepared by (a) forming a prepolymer from hydroxy terminated polybutadiene resin, an aliphatic isocyanate, and a diol containing acid groups; (b) neutralizing the acid; dispersing it in water; and (c) chain extending the prepolymer with a diamine.
U.S. Pat. No. 4,542,012 (Dell) discloses a dermatologically acceptable film-forming composition. The composition comprises (a) a film-forming polymer that is a reaction product of (i) a prepolymer having a plurality of isocyanate functionalities, (ii) a polyvinyl pyrrolidone polymer; and (iii) a chain extender for the prepolymer and the polyvinyl pyrrolidone polymer; and (b) as an anti-microbial agent, iodine, which forms a complex with the film-forming polymer. The polymer so formed is soluble in the hydroalcoholic solvent. The composition, when applied to skin from a fugitive solvent, is capable of forming a substantially water insoluble, tack-free, flexible film that adheres to skin, releases the anti-microbial agent when the film contacts skin. The film exhibits an elongation of at least about 150% and less than about 1000%.
A need exists in the art for polyurethane dispersions that exhibit anti-microbial activity and are stable in alcohol-water solvent systems, where the dispersion has one or more of the following properties: capable of forming stable dispersions in hydro-alcohol systems, capable of rapidly forming films on skin by simple ambient evaporation, and are compatible with antimicrobial agents. Furthermore, films formed by drying down the dispersions exhibit one or more of the following properties: high self adhesion and yet low tack, low humidity sensitivity, high tensile strength, good elongation, transparent, and capable of releasing added antimicrobial agents.
The present invention provides a novel polyurethane-urea dispersion that can be prepared in the presence of and is dispersed in a hydro-alcohol system. As used herein, the term xe2x80x9chydro-alcoholxe2x80x9d refers to solvents based on C1 to C4 lower alcohols mixed with water, where the weight ratio of lower alcohol to water is at least 20:80, preferably at least 40:60, more preferably at least 50:50 and most preferably at least 60:40 by weight. It has been found that rapidly drying dispersions can be formed in hydro-alcohol solvent systems where the ratio of lower alcohol to water is at least 70:30, more preferably at least 80:20 and most preferably at least 85:15 by weight. The preferred lower alcohols include ethanol, 2-propanol, and n-propanol. The term xe2x80x9chydro-alcoholxe2x80x9d is synonymous with the term xe2x80x9calcohol-water.xe2x80x9d
The polyurethane polymer exists as a dispersion in alcohol-water solvent system. As used herein, a xe2x80x9cdispersionxe2x80x9d means generally a two phase system where one phase contains discrete particles distributed throughout a bulk substance, the particles being the disperse or internal phase, and the bulk substance the continuous or external phase. In this invention, the continuous phase is the alcohol-water mixture and at least a portion of the polyurethane exists as the discrete particle. By xe2x80x9cdispersion,xe2x80x9d it is also meant that not necessarily the entire polyurethane polymer needs to be alcohol-water insoluble; at least some of the polymer can be soluble in the alcohol-water mixture. In preferred rapid drying applications, most or all of the polymer is in the dispersed phase. Dispersions are possible through the use of certain components that are insoluble in the alcohol-water solvent system. It is desirable that the dispersion remain stable under ambient conditions. Preferred dispersions are stable at room temperature for more than 30 days, preferably more than 90 days, more preferably for more than 180 days, and most preferably for more than 360 days.
In brief summary, in one aspect, the invention provides a polyurethane dispersion stable in a lower alcohol-water mixture. The dispersion is a reaction product of (a) an isocyanate functional prepolymer comprising the reaction product of: (i) at least one polyactive hydrogen compound, wherein said compound is an alkyl, aryl, or aralkyl structure optionally substituted in and/or on the chain by N, O, S, and combinations thereof, and wherein the compound is insoluble in said lower alcohol-water mixture, when the alcohol to water ratio is at least 50:50 by weight (referred to as the xe2x80x9cAxe2x80x9d component for convenience); (ii) at least one polyisocyanate, and (iii) at least one active hydrogen compound soluble in the alcohol-water mixture, the compound selected from the group consisting of a compound containing an ionic group, a compound containing a moiety capable of forming an anionic group, a compound containing a polyester, polyether, or polycarbonate group having a ratio of 5 or less carbon atoms for each oxygen atom, and mixtures thereof (referred to as the xe2x80x9cBxe2x80x9d component for convenience); and (b) at least one polyfunctional chain extender, where the equivalent ratio of active hydrogen on the chain extender to isocyanate on the isocyanate functional prepolymer is 0.60:1 to 1.20:1.
In one embodiment, the dispersion further comprises anti-microbial agents. Such a dispersion can be used as a liquid drape functioning as a preoperative patient prep. When the dispersion dries to form a film, the film can function as an incise drape.
As used herein, a xe2x80x9cliquid drapexe2x80x9d means a dermatologically acceptable film-forming dispersion that can be applied (e.g., painted or sprayed) onto a patient""s skin. The drape dries on the skin to form a film less than about 10 minutes, preferably less than about 5 minutes, and more preferably less than about 2 minutes upon application at temperatures of about 25xc2x0 to 35xc2x0 C., preferably about 29xc2x0 to 32xc2x0 C. The lower alcohol-water solvent system can function as an effective antimicrobial agent if the ratio of lower alcohol to water is about 60:40 to 90:10. In addition the liquid drape may contain an additional or secondary anti-microbial agent. Secondary antimicrobial agents are generally added to impart persistent antimicrobial activity. The drape preferably has properties, such as elongation of about 100% to 700% and tensile strength greater than about 2.5 lb/inch width for a 1 mil (0.025 mm) thick film. Such properties allow the drape to withstand the stresses imposed on it during certain processes, such as during an operation. For example, in some medical operations, it is common practice for a medical practitioner to apply a liquid drape on the patient at the operation site. After the liquid drape dries and forms a film, the practitioner may make an incision through the drape and the patient""s skin. In some cases, the practitioner may need to widen the incision site. Under such circumstances, the drape should be able withstand the stresses imparted by the incision as well as the widening steps. The drape should also be adhered to the patient""s skin during the entire operation. The drape preferably is not permeable to water or body fluids. In addition, in certain instances, it may be beneficial for the drape to have self adhesion.
As used herein, a material possesses xe2x80x9cself adhesionxe2x80x9d properties when it preferentially adheres to itself or a chemically similar material under pressure or force without the need for significantly elevated temperatures (e.g., without the need for temperatures above about 50xc2x0 C.). Preferred compositions of the invention exhibit self adhesion properties immediately upon contact to itself at room temperature (about 20xc2x0 to 30xc2x0 C.). As used in the previous sentence, the term xe2x80x9cimmediatelyxe2x80x9d means less than a few minutes, e.g., about 5 minutes, preferably less than 1 minute, more preferably less than 30 seconds, depending on the application. A potential benefit of high self adhesion formulations is the ability to coat the same or similar formulations on the underside (patient contact side) of additional patient covering drapes. These drapes can then be fixed in place by simply contacting and optionally pressing them against the dried self adherent incise drape. This can significantly facilitate the draping procedure. Thus, another aspect of the invention involves a kit or a system that contains a drape (or medical materials used on patients during surgery) that has at least a portion coated with the inventive dispersim. Optionally included in the kit is the inventive dispersim in the form of a liquid prep.
An advantage of the invention is the use of oligomeric polyactive hydrogen compounds that are insoluble in the alcohol-water solvent mixture when the ratio of lower alcohol to water is at least 50:50 by wt. Such a compound is typically hydrophobic and provides faster drying and improved hydrolytic stability over prior art liquid drapes. These hydrophobic polyols provide excellent adhesion to skin as well as imparting fluid resistance (such as resistance to water) to the dried film. A further advantage of the inventive dispersion is that it possesses a short cure time, as defined in the Example section. Both short dry time and short cure time are desirable properties in a liquid drape application.
Yet another advantage of the inventive dispersion is that it has low viscosity, high percent solids, able to form hydrophobic films, and is a dispersion. All these factors contribute to short dry time and short cure time, allowing the dispersion to form a film quickly once applied to the skin.